Gas laser oscillator

ABSTRACT

The gas laser oscillator of the invention comprises a discharge tube, a pair of electrodes disposed at both ends thereof, a direct-current high voltage power source for applying a direct-current high voltage in pulse form to the pair of electrodes, an output control device for controlling the direct-current high voltage power source, a fully reflective mirror provided at one end of the outside of the pair of electrodes, a partially reflective mirror disposed at other end of the outside of the pair of electrodes, and an absorber disposed outside of the partially reflective mirror. In thus constituted gag laser oscillator, the output control device controls to apply a same direct-current voltage as during processing between the pair of electrodes also on standby while the absorber is closed. 
     The gas laser oscillator of the invention further comprises a beam splitter outside of the absorber, a switch to be actuated while the beam splitter is installed at a specified position, a focusing lens disposed on the optical axis of the laser beam reflected and separated by the beam splitter, a shielding plate disposed so as to open or close the passage of laser beam, a switch to be actuated while the shielding plate is open, a detector for detecting the laser beam, an amplifier for amplifying the output of the detector, and a medium passage disposed in contact with the detector for realizing heat exchange between the temperature-controlled medium and the detector, whereby it is controlled to issue the laser beam only while the beam splitter is installed at a specified position. The output of the laser beam is controlled so that the detector input may not exceed the maximum allowable input of the detector while the shielding plate is open. Moreover, the beam splitter, focusing lens, and detector are arranged so that the optical axis may be horizontal to the laser beam passing therethrough.

This application is a divisional application of application Ser. No.09/123,357, filed Jul. 28, 1998.

BACKGROUND OF THE INVENTION

The present invention relates to a gas laser oscillator low influctuation rate of laser beam, capable of producing laser beam stably,and free from malfunction.

First, a conventional gas laser oscillator is described by referring toFIG. 11. In FIG. 11, reference numeral 1 is a discharge tube for forminga discharge space 5 inside, and the inside of the discharge tube 1 isfilled with laser gas, or laser gas is circulating by a circulatingdevice not shown in the drawing. Reference numeral 2 is an electrodeprovided at one end of the discharge tube 1, 3 is an electrode providedat other end of the discharge tube 1, 4 is a direct-current high voltagepower source for applying a voltage for discharging between theelectrodes 2 and 3, and 6 is a fully reflective mirror, which iscombined with a partially reflective mirror 7 to compose an opticalresonator for amplifying the laser light. Reference numeral 9 is anoutput control device for controlling the direct-current high voltagepower source 4.

This is the basic constitution of the gas laser oscillator. In thusconstituted gas laser oscillator, the operation of its basic portion isdescribed below. First, according to the command from the output controldevice 9, a direct-current high voltage in pulse form is applied betweenthe electrodes 2 and 3 from the direct-current high voltage power source4 for discharging between the electrodes 2 and 3. By this dischargeenergy, the laser gas in the discharge space 5 is excited. The excitedlaser gas is set in resonant state by the optical resonator composed ofthe fully reflective mirror 6 and partially reflective mirror 7, and thelight is amplified, and a laser beam 8 is issued from the partiallyreflective mirror 7. The produced laser beam 8 is used in laserprocessing such as cutting and piercing.

In such gas laser oscillator, also on standby while not processing,discharge occurs in the discharge tube 1, and the laser beam 8 is issuedfrom the partially reflective mirror 7 at a preset output level.However, since an absorber 10 is disposed ahead of the partiallyreflective mirror 7, the produced laser beam 8 is intercepted by theabsorber 10 and does not leak outside.

When processing by the laser beam 8, by the command from an absorbercontrol device 12, an absorber drive device 11 operates the absorber 10,and the passage of laser beam 8 is opened, and the laser beam 8 isemitted outside to process the workpiece 15.

On the other hand, at the side closer to the workpiece 15 from theabsorber 10 on the optical axis of the laser beam 8, a beam splitter 14is disposed. The laser beam 8 is separated by this beam splitter 14, andthe straightforward portion 8 a reaches the workpiece 15, and processesby cutting or piercing. The portion 8 b reflected and separated by thebeam splitter 14 is focused by a focusing lens 16, and irradiates adetector 17. The detector 17 irradiated by the separated portion 8 bdetects that the laser beam 8 is being emitted. This detection signal isamplified by an amplifier 18, and is issued from a terminal 19.

However, the conventional gas laser oscillator as explained above hadseveral problems.

First was a problem of fluctuation of laser beam output in a transientstate from standby by cutting off the laser beam 8 by the absorber 10 toprocessing by passing the laser beam 8 by setting aside the absorber 10.That is, in the standby state (A) as shown in FIG. 7, a signal forobtaining an output of low level necessary for maintaining discharge isissued from the output control device 9, and a direct-current highvoltage corresponding to the signal level is applied between theelectrodes 2 and 3 to maintain discharge. Once a processing start signalis entered and the absorber 10 is opened to be in state (B), theprocessing start signal 13 is sent from the absorber control device 12into the output control device 9. Receiving this signal 13, the outputcontrol device sends out a signal having level and waveform necessaryfor obtaining the output of pulse laser beam 8 suited to the purpose ofprocessing. In the conventional control, however, since the dischargestate in the discharge space 5 on standby is different from thedischarge state in the discharge space 5 during processing, thedissociation state of laser gas is different between processing andstandby. It hence takes time until the dissociation state of laser gasis stabilized from start of processing and fluctuations of laser outputin the initial period of processing are large so that stable processingis disabled. Upon start of processing, further, it takes time tostabilize owing to the presence of unstable period due to heat effectsof the fully reflective mirror 6 and partially reflective mirror 7 forcomposing the optical resonator and unstable period of surface state ofthe electrode 2 and electrode 3, which is also a cause of unstableoutput of the laser beam 8 in the initial period of processing. Thisunstable output of the laser beam 8 in the initial period of processingwas a serious problem in processing for a short time, in particular.

Other problem is related to the laser beam detecting device that isindispensable for accurate control of the gas laser oscillator. In theconventional constitution shown in FIG. 11, after dismounting the beamsplitter 14 for the purpose of adjustment of gas laser oscillator or thelike, if laser processing is done without reassembling the beam splitter14, the laser beam 8 not attenuated by the beam splitter 14 directlyirradiates to the workpiece 15. As a result, the workpiece is irradiatedwith an exessive laser beam 8, and processing failure may occur.

Or, when adjusting the gas laser oscillator, if a laser beam 8 over theallowable capacity of the detector 17 is irradiated by mistake, thedetector 17 may be broken.

Further, the detector 17 may fluctuate in the detecting sensitivity dueto fluctuations of temperature depending on heat generation by incidentof laser beam 8 b or ambient temperature. Fluctuation of detectingsensitivity of the detector 17 may cause output of wrong information.For example, if the detecting sensitivity is raised, although laser beam8 is not emitted, it may be falsely recognized that the laser beam 8 isemitted, or if the detecting sensitivity is lowered, although the laserbeam is emitted, it may be falsely recognized that the laser beam 8 isnot emitted. Hence, accurate control of the gas laser oscillator may bedisabled.

Still more, if used for a long period, dust may deposit on the beamsplitter 14, focusing lens 16, or detecting surface of the detector 17,and the detecting sensitivity may be lowered.

SUMMARY OF THE INVENTION

The invention is hence devised to solve the above plural problems, andit is a first object thereof to transfer promptly to a state of stableand favorable laser processing by eliminating the unstable period oflaser beam output in the transient state of changing from standby toprocessing.

It is a second object to solve the problems relating to laser beamdetector, including prevention of processing failure by irradiation oflaser beam of excessive energy to the workpiece if forgetting to mountthe beam splitter, prevention of damage of the detector due to excessiveinput to the detector by wrong adjustment, and prevention of wrongcontrol of gas laser oscillator due to malfunction of detector caused byfluctuations of detector temperature or deposit of dust.

To achieve the objects, the gas laser oscillator of embodiment 1 of theinvention comprises:

a discharge tube for forming a discharge space inside,

a fully reflective mirror disposed toward the opening at one end of thedischarge space for composing an end mirror,

a partially reflective mirror disposed toward the opening at other endof the discharge space for composing an output mirror,

a pair of electrodes disposed at both ends of the discharge tube,

a direct-current high voltage power source for discharging in thedischarge space by applying a high voltage of pulse form between thepair of electrodes,

an output control device for Controlling the output of thedirect-current high voltage power source,

a movable absorber disposed outside of the partially reflective mirrorfor opening and closing the passage of laser beam,

a drive device for driving to open or close the absorber, and

an absorber control device for controlling the drive device so as tomove the absorber to a position for intercepting the laser beam onstandby, and to move to a position so that the absorber may notinterfere passing of laser beam during processing,

in which the output control device controls the direct-current highvoltage power source so as to discharge in the same condition both uponstandby and during processing.

The gas laser oscillator of embodiment 2 of the invention comprises:

a discharge tube for forming a discharge space inside,

a fully reflective mirror disposed toward the opening at one end of thedischarge space for composing an end mirror,

a partially reflective mirror disposed toward the opening at other endof the discharge space for composing an output mirror,

a pair of electrodes disposed at both ends of the discharge tube,

a direct-current high voltage power source for discharging in thedischarge space by applying a high voltage of pulse form between thepair of electrodes,

an output control device for controlling the output of thedirect-current high voltage power source,

a beam splitter disposed outside of the partially reflective mirror soas to cut across the passage of laser beam for separating the laserbeam,

a switch which is actuated when the beam splitter is installed at aspecified position,

a focusing lens for focusing the laser beam separated by reflection bythe beam splitter,

a detector for detecting the laser beam focused by the focusing lens,

an amplifier for amplifying the output of the detector and issuing asignal to the output control device,

a shielding plate disposed between the focusing lens and detector foropening and closing, and

a switch which is actuated when the shielding plate is opened.

In the gas laser oscillator of embodiment 2, preferably, the outputcontrol device controls the direct-current high voltage power source sothat the laser beam may be emitted only while the switch which isactuated when the beam splitter is installed at a specified position isbeing actuated.

In the gas laser oscillator of embodiment 2, preferably, the outputcontrol device controls the direct-current high voltage power source soas not to emit a laser beam exceeding the maximum allowable input of thedetector while the switch which is actuated when the shielding plate isopened is being actuated.

In the gas laser oscillator of embodiment 2, preferably, the detector isprovided with a passage of medium so as to exchange heat with themedium, and the detector is controlled of temperature by the mediumcontrolled of temperature.

In the gas laser oscillator of embodiment 2, preferably, the beamsplitter, the focusing lens, and the detector are disposed so that theaxis of laser beam passing therethrough may be in the horizontaldirection.

According to the gas laser oscillator of embodiment 1, it is controlledso as to emit laser beam of same pulse width and same pulse frequency atsame output level whether on standby or during processing, and the laserbeam is prevented from escaping outside by the absorber, and therefore,on standby, the dissociation state of laser gas is same as duringprocessing, and it does not take time to stabilize the dissociationstate upon start of processing. Moreover, the temperature of partiallyreflective mirror and fully reflective mirror and surface state of theelectrodes are same on standby and during processing, and transientunstable state does not occur upon start of processing, and the laseroutput is not unstable in the initial period of processing, so thatfavorable laser processing may be done.

According to the gas laser oscillator of embodiment 2, laser is notproduced unless the beam splitter is installed at specified position,and therefore the workpiece is not irradiated with laser beam notattenuated by the beam splitter, and processing failure due toapplication of excessive input to the workpiece is avoided. Moreover,while the shielding plate is open, it is controlled so as not to emitthe laser beam exceeding the maximum allowable input of the detector,and the detector is not broken by excessive input. Still more, since thedetector is controlled of temperature by the medium controlled oftemperature, the temperature of the detector is not changed by the inputof laser beam or ambient temperature, and a stable detecting sensitivityis obtained. Moreover, since the beam splitter, focusing lens anddetector are installed so that the optical axis of the laser beampassing through the beam splitter, focusing lens and detector may behorizontal, deposit of dust on the reflecting surface of the beamsplitter, surface of the focusing lens, and detecting surface of thedetector is lessened, reduction of the sensitivity of the detector inthe time course are improved notably, and a stable detecting sensitivityis obtained for a long period.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a structural diagram showing an entire gas laser oscillator ofthe invention.

FIG. 2 is a structural diagram showing embodiment 1 of gas laseroscillator of the invention.

FIG. 3 is a characteristic diagram showing the state of command signalbefore and after start of processing in embodiment 1 of the invention.

FIG. 4 is a characteristic diagram showing the relation of output levelon standby and fluctuation ratio of laser peak output during processingin embodiment 1 of the invention.

FIG. 5 is a characteristic diagram showing the relation of pulse widthon standby and fluctuation ratio of laser peak output during processingin embodiment 1 of the invention.

FIG. 6 is a characteristic diagram showing the relation of pulsefrequency on standby and fluctuation ratio of laser peak output duringprocessing in embodiment 1 of the invention.

FIG. 7 is a characteristic diagram showing the state of command signalbefore and after start of processing in a conventional gas laseroscillator.

FIG. 8 is a structural diagram showing embodiment 2 of gas laseroscillator of the invention.

FIG. 9 is a characteristic diagram showing changes of detector output inthe gas laser oscillator in embodiment 2 of the invention and in theprior art.

FIG. 10 is a characteristic diagram showing time-course changes ofdetector output in the gas laser oscillator in embodiment 2 of theinvention and in the prior art.

FIG. 11 is a structural diagram showing an entire conventional gas laseroscillator.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 2 shows a constitution of a portion relating to embodiment 1 of theinvention, and FIG. 8 shows a constitution of embodiment 2 of theinvention. FIG. 1 shows an entire constitution of the inventioncombining the portion relating to embodiment 1 in FIG. 2 and the portionrelating to embodiment 2 in FIG. 8.

EMBODIMENT 1

Referring now to FIG. 2, embodiment 1 of the gas laser oscillator of theinvention is described below. Reference numerals used in FIG. 2 are sameas in FIG. 11 relating to the prior art. Although partly duplicatingwith the description in FIG. 11, FIG. 2 is newly explained.

In FIG. 2, reference numeral 1 is a discharge tube 1 for forming adischarge space 5 inside, and the inside of the discharge tube 1 isfilled with laser gas, or laser gas is circulating by a circulatingdevice not shown in the drawing. Reference numeral 2 is an electrodeprovided at one end of the discharge tube, 3 is an electrode provided atother end of the discharge tube, 4 is a direct-current high voltagepower source for applying a voltage for discharging between theelectrodes 2 and 3, and 6 is a fully reflective mirror, which iscombined with a partially reflective mirror 7 to compose an opticalresonator for amplifying the light. Reference numeral 9 is an outputcontrol device for controlling the direct-current high voltage powersource 4.

In thus constituted gas laser oscillator, the operation is describedbelow. First, according to the command from the output control device 9,a high voltage direct-current voltage in pulse form is applied betweenthe electrodes 2 and 3 from the direct-current high voltage power source4 for discharging between the electrodes 2 and 3. By this dischargeenergy, the laser gas in the discharge space 5 is excited. The excitedlaser gas is set in resonant state by the optical resonator composed ofthe fully reflective mirror 6 and partially reflective mirror 7, and thelaser light is amplified, and a laser beam 8 is issued from thepartially reflective mirror 7. The produced laser beam 8 is used inlaser processing such as cutting and piercing.

In such gas laser oscillator, also on standby while not processing,discharge occurs in the discharge tube 1, and the laser beam 8 is issuedfrom the partially reflective mirror 7 at a preset output level.However, since an absorber 10 is disposed ahead of the partiallyreflective mirror 7, the produced laser beam 8 is intercepted by theabsorber 10 and does not leak outside.

FIG. 3 shows the relation of opening and closing of the absorber 10 andthe state of signal issued from the output control device 9 in theprocess from standby to processing. First, on standby, the absorber 10is closed, and the laser beam 8 is intercepted of its passage by theabsorber 10, and is not produced outside. At this time, from the outputcontrol device 9, a signal for commanding same level, same pulse widthand same pulse frequency as during processing is sent to the outputcontrol device 9. At processing start point T₀, the absorber 10 isopened, and the laser beam 8 is issued to outside, and reaches theworkpiece 15 to process it.

Stability of output of the gas laser oscillator thus controlled isdescribed below. FIG. 4 shows changes of fluctuation ratio of outputpeak value of laser beam by changing only the output level of pulse,while keeping constant the pulse width and pulse frequency of the highvoltage direct-current voltage applied between the electrode 2 andelectrode 3. The axis of abscissas denotes the output level of pulse,and the axis of ordinates represents the fluctuation ratio of the outputpeak value of laser beam. The value indicated by broken line on the axisof abscissas shows the value of pulse output level used in processing.As clear from this graph, when the output level on standby is same asthe output level during processing, the fluctuation ratio of output peakvalue of laser beam is minimum. The larger the difference between theoutput level upon standby and the output level during processing, thegreater is the fluctuation ratio of the output peak value of laser beam.Therefore, it is known most preferable that the output level on standbyshould be set same as the output level during processing.

FIG. 5 shows changes of fluctuation ratio of output peak value of laserbeam by changing only the pulse width, while keeping constant the outputlevel and pulse frequency of the high voltage direct-current voltageapplied between the electrode 2 and electrode 3. The axis of abscissasdenotes the pulse width, and the axis of ordinates represents thefluctuation ratio of the output peak value of laser beam. The valueindicated by broken line on the axis of abscissas shows the value ofpulse width used in processing. As clear from this graph, when the pulsewidth on standby is same as the pulse width during processing, thefluctuation ratio of output peak value of laser beam is minimum. Thelarger the difference between the pulse width upon standby and the pulsewidth during processing, the greater is the fluctuation ratio of theoutput peak value of laser beam. Therefore, it is known most preferablethat the pulse width on standby should be set same as the pulse widthduring processing.

FIG. 6 shows changes of fluctuation ratio of output peak value of laserbeam by changing only the pulse frequency, while keeping constant theoutput level and pulse width of the high voltage direct-current voltageapplied between the electrode 2 and electrode 3. The axis of abscissasdenotes the pulse frequency, and the axis of ordinates represents thefluctuation ratio of the output peak value of laser beam. The valueindicated by broken line on the axis of abscissas shows the value ofpulse frequency used in processing. As clear from this graph, when thepulse frequency on standby is same as the pulse frequency duringprocessing, the fluctuation ratio of output peak value of laser beam isminimum. The larger the difference between the pulse frequency uponstandby and the pulse frequency during processing, the greater is thefluctuation ratio of the output peak value of laser beam. Therefore, itis known most preferable that the pulse frequency on standby should beset same as the pulse frequency during processing.

In embodiment 1 of the gas laser oscillator of the invention, on,standby while not processing by laser beam, it is controlled to generatelaser beam by applying a direct-current high voltage of same outputlevel, pulse width and pulse frequency as during processing between theelectrodes. Therefore, as explained above, a stable laser beam small influctuation of output peak value is obtained, and laser processing ofhigh quality is enabled.

EMBODIMENT 2

Referring now to FIG. 8, embodiment 2 of the gas laser oscillator of theinvention is described below. Reference numerals used in FIG. 8 are sameas in, FIG. 11 relating to the prior art. Although partly duplicatingwith the description in FIG. 11, embodiment 2 is described below.

In FIG. 8, reference numerals 1 to 9 are same as in the function andoperation in embodiment 1 and their explanation is omitted. FIG. 8,reference numeral 14 is a beam splitter disposed on the optical axis ofthe laser beam. The laser beam 8 is separated by this beam splitter 14,and the straightforward portion 8 a reaches the workpiece 15 to be usedin processing. The portion 8 b reflected and separated by the beamsplitter 14 is focused by a focusing lens 16, and irradiates a detector17. The detector 17 irradiated by the separated portion 8 b detects thatthe laser beam 8 is being emitted. The signal detected by the detector17 is amplified by an amplifier 18, and is issued from a terminal 19.

Reference numeral 20 is a switch to be actuated when the beam splitter14 is installed at a specified position, and sends an actuated signal toa terminal 21 when the beam splitter 14 is installed at a specifiedposition The signal of this terminal 21 is sent into the output controldevice 9. The output control device 9 controls so that the laser beam 8may be emitted only while the switch 20 is being actuated, that is,while the beam splitter 14 is installed at a specified position.

By thus controlling, the laser beam 8 is not emitted while the beamsplitter 14 is being removed. It hence prevents the laser beam 8 havingan excessive laser energy not attenuated by the beam splitter 14 frombeing applied directly to the workpiece 15. It hence avoids processingfailure due to application of excessive energy.

In FIG. 8, reference numeral 22 is a shielding plate disposed on theoptical axis of the laser beam 8 reflected and separated by the beamsplitter 14, and only when the shielding plate 22 is opened, the lagerbeam 8 b reaches the detector 17. Reference numeral 23 is a switch whichoperates while the shielding plate 22 is open, and the actuated signalof the switch 23 is issued to a terminal 24. The signal of this terminal24 is sent into the output control device 9. The output control device 9controls the maximum output of the laser beam 8 so that the energy ofthe laser beam 8 b may not exceed the maximum allowable input of thedetector 17 while the switch 23 is being actuated, that is, while theshielding plate 22 is open.

Therefore, the detector 17 is not provided with energy larger than themaximum allowable input, and the detector 17 is not damaged byirradiation of excessive energy.

Further, in FIG. 8, reference numeral 25 is a passage for passing mediumsuch as oil. The passage 25 is provided in contact with the detector 17so that heat exchange between the medium and the detector 17 may be doneefficiently. By controlling the temperature of the medium passingthrough this passage 25, the temperature of the detector 17 is keptconstant.

FIG. 9 shows the stability of output of the detector controlled oftemperature. In FIG. 9, the axis of abscissas denotes the time (unit:minutes), and the axis of ordinates represents the output level. In thediagram, A shows the temperature-controlled state of the detector 17 bythe medium, and B shows the non-controlled state of the detector 17. Inthe non-controlled state B of the detector 17, as the time passes, theoutput level of the detector 17 hardly changes, but in thetemperature-controlled state A of the detector 17 by medium, the outputlevel of the detector 17 slightly changes. Incidentally, the broken lineC shows the state of output level free from fluctuation.

Therefore, by passing temperature-controlled medium into the passage 25and controlling the temperature of the detector 17, the output level ofthe detector 17 is stabilized by eliminating the effects of ambienttemperature or laser beam irradiation. By stabilizing the output levelof the detector 17, it is judged correctly whether the laser beam isemitted or not, so that highly reliable control of the gas laseroscillator is realized.

As shown in FIG. 8, the beam splitter 14, focusing lens 16, shieldingplate 24, and detector 17 are disposed in series on the optical axis ofthe laser beam 8 b, but in this embodiment, these components arearranged in the horizontal direction. That is, the components aredisposed so that the optical axis of the laser beam 8 b may be directedin the horizontal direction. In such arrangement, the reflection surfaceof the beam splitter. 14, both surfaces of the focusing lens 16, and thedetection surface of the detector 17 are parallel to the vertical ornearly vertical plane, and therefore deposit of dust on the passingsurface of laser beam 8 b of these components may be suppressed. Sincedeposit of dust is suppressed, the output level of the detector 17 maybe smaller in changes in the time course.

FIG. 10 shows changes of the output level of the detector 17 in the timecourse. In FIG . 10, the axis of abscissas denotes the time (unit:hours), and the axis of ordinates represents the output level of thedetector. In the diagram, B shows a case in which the optical axis ofthe laser beam 8 b is directed in the vertical direction, and A shows acase in which the optical axis of the laser beam 8 b is directed in thehorizontal direction. As clear from FIG. 10, when the beam splitter 14,focusing lens 16, shielding plate 22 and detector 17 are arranged in thehorizontal direction, changes of output level of the detector 17 in thetime course are extremely smaller as compared with the case ofarrangement in the vertical direction. Incidentally, the broken line Cin the diagram indicates the state free from fluctuations in the outputlevel.

Therefore, when the beam splitter 14, focusing lens 16, shielding plate22 and detector 17 are arranged in the horizontal direction, the outputlevel of the detector 17 can be stabilized for a long period, so thatthe gas laser oscillator can be controlled at high reliability withoutmalfunction.

What is claimed is:
 1. A gas laser oscillator comprising: a dischargetube for forming a discharge space inside, a fully reflective mirrordisposed toward the opening at one end of said discharge space forcomposing an end mirror, a partially reflective mirror disposed towardthe opening at other end of said discharge space for composing an outputmirror, a pair of electrodes disposed at both ends of said dischargetube, a direct-current high voltage power source for discharging in saiddischarge space by applying a high voltage of pulse form between saidpair of electrodes, an output control device for controlling the outputof said direct-current high voltage power source, a beam splitterdisposed outside of said partially reflective mirror so as to cut acrossthe passage of laser beam for separating the laser beam, a switch to beactuated when said beam splitter is installed at a specified position, afocusing lens for focusing the laser beam separated by reflection bysaid beam splitter, a detector for detecting the laser beam focused bysaid focusing lens, an amplifier for amplifying the output of saiddetector and issuing a detection signal, a shielding plate disposedbetween the focusing lens and detector for opening and closing, and aswitch to be actuated when the shielding plate is opened.
 2. A gas laseroscillator of claim 1, wherein said output control device controls saiddirect-current high voltage power source so that the laser beam may beemitted only while the switch to be actuated when said beam splitter isinstalled at a specified position is being actuated.
 3. A gas laseroscillator of claim 1, wherein said output control device controls saiddirect-current high voltage power source so as not to emit a laser beamexceeding the maximum allowable input of said detector while the switchto be actuated when said shielding plate is opened is being actuated. 4.A gas laser oscillator of claim 1, wherein passage of medium controlledof temperature is provided so as to exchange heat with said detector,and said detector is controlled of temperature by the medium controlledof temperature.
 5. A gas laser oscillator of claim 1, wherein said beamsplitter, said focusing lens, and said detector are disposed so that theaxis of laser beam passing therethrough may be in the horizontaldirection.